The Applicant has invented a printhead chip which is capable of printing text and images at a resolution of up to 1600 dpi. While developing this technology, the Applicant has filed many patent applications covering various inventions which have been conceived during this development.
A large proportion of the inventions are in the field of micro electro-mechanical systems. These systems allow up to 84000 nozzle arrangements to be formed on a single printhead chip. As a result of various constraints arising from a necessity for the high density of nozzle arrangements, it has been necessary to design the systems in such a way that each nozzle arrangement, in most cases, includes one or more moving parts which serve to eject ink from each of the nozzle chambers defined by the nozzle arrangements.
In most cases, these moving parts or components act on the ink within a nozzle chamber to eject that ink from the nozzle chamber. The Applicant has identified a particular difficulty to be overcome in the manufacture of such printheads. This has to do with the back flow of ink which is highly undesirable. The back flow of ink usually occurs after an ink drop has been ejected from a particular nozzle arrangement where a resulting break off of the drop and “suck back” of the ink into the nozzle chamber causes this back flow. Further, this back flow can also arise as a result of the operation of ink ejection mechanisms of such printheads. Many of the ink ejection mechanisms that the applicant has developed incorporate a reciprocal movement of one or more components. This reciprocal movement of the components can result in a back flow of ink as the components return to a start condition once a drop has been ejected.
It will be appreciated that since the ink is physically ejected from each nozzle arrangement by the movement of the nozzle components it is extremely important that a consistent and correct amount of ink be supplied to each of the nozzle chambers. The back flow which can result in the absence of any mechanism to prevent it can disturb the fine balance required to achieve the accurate supply of ink to the various nozzle arrangements.
Attempts have been made to address the problem of back flow in other forms of printheads such as thermal ink jet printheads. An example of such an attempt is indicated in FIG. 1 of the drawings. Here, reference numeral 1 generally indicates part of a thermal ink jet printhead incorporating a back flow prevention mechanism. This printhead 1 includes an actuator in the form of a heater 2 which is positioned in a substrate 3 defining a floor 4 of a nozzle chamber 5. An ink ejection port 6 is positioned above the heater 2. The heater 2 heats ink 7 to an extent which is such that the ink 7 is ejected from the ejection port 6. It will readily be appreciated that back flow of the ink in this case would inhibit the ejection of the ink 7 due to the loss of the required ejection pressure. Thus, a passive flap 8 is positioned in the chamber 5. The flap 8 is configured to bend towards a roof 9 of the nozzle chamber 5 when acted upon by the ink 7, thereby obstructing a possible back flow of ink.
This form of back flow prevention device is not suitable for an ink jet printhead of the type described in this specification. The primary reason for this is that the operation of the device is dependent upon the heating of the ink. This form of printhead does not utilize the heating of ink to operate. Further, Applicant has found that it is highly advantageous to incorporate a back flow prevention device in an actuator mechanism so that a number of moving components can be kept to a minimum.
The Applicant has conceived the present invention to at least reduce the level of back flow occurring once ink has been ejected from the nozzle chamber, while maintaining a suitably low level of energy consumption.